All behavior involves choice and many social and health problems arise from bad or self-destructive choices. Experimental research on free-operant choice behavior over the past 40 years is based on the idea that response rate or choice probability is determined by the value of outcomes. The simplest case is concurrent schedules where the organism is confronted with a free choice between two or more response alternatives and choices are reinforced directly with primary reinforcement. When the reinforcement schedules are variable-interval (VI), the usual result is the so-called matching law: relative response rates match relative reinforcement rates. A more complex case is when the choices are reinforced not with food but by the appearance of a second stimulus in the presence of which food is delivered according to another schedule (concurrent chain schedules). These experiments are usually thought of as studies of conditioned or secondary reinforcement - and results do not fit the matching law. Several alternatives have been proposed, but all of them use response rate in the choice link as dependent variable, and some measure of 2nd - link value as independent variable. Almost none of these experiments or theories has addressed the problem of fixed- (as opposed to variable-) interval choice links nor do they deal with dynamics or explain behavior in non-choice chain experiments. Yet there must be common principles underlying these varied performances. The research for which support is requested in this proposal began with a longstanding puzzle on simple chain schedules: unstable behavior, even the complete cessation of responding, in early links of a multi-link chain, even when individual links are relatively short. This effect seemed to us to be explainable, in general if not in detail, by a process we had studied for many years called linear waiting: that organisms on interval schedules will wait before responding for a time proportional to the just-experienced time to reinforcement (TTR). This led us to conjecture that perhaps behavior on concurrent chain schedules is mainly controlled not by the value of outcomes, i.e., by conditioned reinforcement, buy simply by TTR, as we had found for a simple interval and chain schedules. A reviewer suggested that this idea is unlikely to apply to simple concurrent VI-VI schedules, where the TTR may be very short and waiting time (WT) is comparably short. But in this revised proposal we present striking new data showing unequivocally that relative waiting time on concurrent chain schedules, and even on simple concurrent VI-VI schedules, is highly correlated with measures of preference. Moreover, WT seems to behave in a similar way on all interval schedules and thus offers the possibility of a truly general approach to choice behavior that incorporates simple as well as concurrent and fixed- as well as variable-interval schedules. We also present new data on a version of specialized chain schedule known as the time-lift (T-L) procedure, which has played a key role in promoting a representational view of interval timing as a linear-scaled process. The T- L procedure has been criticized recently on both theoretical and experimental grounds. Our new experiment shows that the TTR idea seems to apply here also and the T-L experiment indeed can not (as originally claimed) prove that "subjective time" is or is not linear. We propose a total of 12 experiments to explore the further implications of these findings for the dynamics of behavior on simple and concurrent interval schedules of reinforcement. We believe that these studies may lead to an entirely new unified approach to choice.